Python Checkbutton reads value only once

Question

Python Checkbutton reads value only once

I've looked in StackOverflow for any similar problems, but the only one that looked similar was this here. It suggested that in this case the variable should be set global but I don't think that's a good solution. So I'm asking you guys for a better one.

I want to use Checkbutton() in Python and my code looks (simplified) like this...

#!/usr/bin/env

from Tkinter import *

Fenster = Tk()
Fenster.title ("Sensors")

Number = IntVar()
Button = Checkbutton(Fenster, text = "Check me", variable = Number, onvalue = 1, offvalue = 0)

print Number.get()

Button.pack()

mainloop()

When i run this code, the window opens and i see the Checkbox. So far so good. But when I want to check or uncheck it, the value of "Number" somehow doesn't change. It only displays "1", probably from the first frame, and never changes.

Could you give me some advice how to improve this?

Reblochon Masque · Accepted Answer · 2018-08-06 09:53:40Z

1

You need to check the value of number; you can do this by assigning a command to print number, when the button is clicked:

import tkinter as tk   # <-- avoid star imports

def f():
    print(number.get())

fenster = tk.Tk()
fenster.title ("Sensors")

number = tk.IntVar()
button = tk.Checkbutton(fenster, text="Check me", variable=number, command=f)

button.pack()

fenster.mainloop()   # call mainloop on your root window

answered Aug 6, 2018 at 9:53

Reblochon Masque

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3 Comments

Quotenbanane Over a year ago

Worked perfectly, thanks. But why isn't the original code working? With mainloop() shouldn't the code print the value again and again each frame?

Reblochon Masque Over a year ago

No, mainloop keeps the gui responsive and listening to interactions; it does not run arbitrary code on its own.

Quotenbanane Over a year ago

Oh okay, thanks a lot. All questions've been answered.

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Python Checkbutton reads value only once